Channel capacity of telecommunication systems is doubled by transmitting independent signals within the same frequency band in orthogonal polarizations. Isolation between signals of these orthogonal polarizations is diminished by atmospheric and other effects such as rain depolarization, Faraday rotation in the ionosphere, and imperfect antenna alignment. Reduction of the isolation between orthogonally polarized signals increases cross-coupling between the polarized signals. Cross-coupling is a source of interference which seriously degrades service quality of a telecommunication system.
Cross-polarization interference cancellation has been proposed as a suitable means of reducing interference caused by coupling between a cross-polarized signal and the signal of interest. See, for example, the cross-polarization interference cancelers suggested in the articles of Y. Bar-Ness et al., "Cross Coupled Boatstrapped Interference Canceler," Int. Conf. on Antennas and Propagation, Vol. I, pp. 292-5 (1981) and D. Brandwood, "Cross-Coupled Cancellation System for Improving Cross-Polarisation Discrimination," Int. Conf. on Antennas and Propagation, Part I, pp. 41-5 (1978).
Many cross-polarization interference cancelers include correlators or power detectors to provide cancellation performance measure signals which are used to control the operation of the canceler circuit (see FIG. 1). In order to generate the performance measure signals, these circuits generally include a plurality of square law devices. Mismatching between square law devices leads to errors such as DC offset in the performance measure signals which, in turn, limit the accuracy and overall performance of the interference canceler.